Date   : Mon, 26 Jul 2010 12:33:10 +0100
From   : jgh@... (J.G.Harston)
Subject: Spitting expletives

Rick Murray wrote:
>> As the SBC operation is effectively A = A - operand, a borrow occurs if
>> the operand is larger than A.
>
> Mmmm, sounds like CMP's logic for the N flag. As I'm coding this, I'm

CMP and SBC are exactly the same, except 1) there's no carry-in and
2) the result is not stored, only the flag effects.

> This, actually, is a point raised in the FDC emulation:
>    Latch.FDCDiscDensity = Not ((Value And 16) = 16) ' INVERTED
[etc]

Not as bad as the Speech system where some combination of events
(Acorn programmed thousands of PHROMs wrong?) byte data has to
be reversed before being sent.

-- 
J.G.Harston - jgh@...